The present invention relates to a gear-shift device for a change-speed gearbox that has shift gates, comprising a shift-control housing having a geometrical principal axis, and a selector shaft kinematically coupled to a manual-shift lever and supported in an axially displaceable manner in the shift-control housing, coaxially with the principal axis of the shift-control housing. A sleeve-shaped stop part, a pin-shaped stop part, a reaction sleeve and a cylindrical return spring are each arranged coaxially with the principal axis. One of the stop parts is fixed in terms of motion with the selector shaft and the other of said stop parts is fixed in terms of motion with the shift-control housing, and the stop parts are mutually concentric to form an annular space therebetween. At least one reaction ball is provided, with the reaction sleeve, the reaction ball and the return spring being accommodated in the annular space between the mutually concentric stop parts. The sleeve-shaped stop part has a radial guide against which the reaction balls can be brought to rest in a first direction of the principal axis. The reaction sleeve has an inclined surface on a first end against which the reaction balls can be brought to rest in a second direction of the principal axis. The pin-shaped stop part has an axial abutment and the reaction sleeve has a second end used as an axial abutment and is supported by this second end, with the interposition of the return spring, against the axial abutment of the pin-shaped stop part. The pin-shaped stop part has a narrow pin section and a wide pin section, with a transition therebetween, the transition being an inclined surface against which the reaction balls come to rest when the selector shaft is actuated in the direction of the principal axis into one of three positions each assigned to a particular shift gate of the change-speed gearbox. The reaction balls are supported centripetally against the wide pin section after being displaced radially along the inclined surface on the pin-shaped stop part when the selector shaft is actuated into a second position lying adjacent to the first position in the direction of the principal axis, and the reaction sleeve is displaced in the direction of the abutment of the return spring by the reaction balls cooperating with the inclined surface of the reaction sleeve, the abutment of the return spring being fixed in terms of motion relative to the pin-shaped stop part. A third position of the selector shaft lies adjacent to a first position in the direction of the principal axis opposite to the second position.
A known gear-shift device, of the type described above, is shown in U.S. Pat. No. 3,164,030. As seen in FIG. 4 of that patent, the reaction sleeve, which is under a continuous spring force, exerts a force in all positions of the selector shaft, via its inclined surface and the reaction balls, on the pin-shaped stop part connected to the selector shaft in a manner fixed in terms of motion relative to it. This force thus makes itself felt as a resistance at the manual-shift lever even when the shift gate for the reverse gear is not being selected whereas the whole point of the arrangement is to make a working point felt at the manual-shift lever when selecting the shift gate for the reverse gear.
An object of the present invention is, in a gear-shift device of the general type initially described, to avoid the occurrence of unwanted resistances at the manual-shift lever when the shift gate to be marked by a working point is not being selected.
This and other objects are achieved by the present invention which provides a gear-shift device for a change-speed gearbox that has shift gates, comprising a shift-control housing having a geometrical principal axis, and a selector shaft kinematically coupled to a manual-shift lever and supported in an axially displaceable manner in the shift-control housing, coaxially with the principal axis of the shift-control housing. A sleeve-shaped stop part, a pin-shaped stop part, a reaction sleeve and a cylindrical return spring are each arranged coaxially with the principal axis. One of the stop parts is fixed in terms of motion with the selector shaft and the other of said stop parts is fixed in terms of motion with the shift-control housing, and the stop parts are mutually concentric to form an annular space therebetween. At least one reaction ball is provided, with the reaction sleeve, the reaction ball and the return spring being accommodated in the annular space between the mutually concentric stop parts. The sleeve-shaped stop part has a radial guide against which the reaction balls can be brought to rest in a first direction of the principal axis. The reaction sleeve has an inclined surface on a first end against which the reaction balls can be brought to rest in a second direction of the principal axis. The pin-shaped stop part has an axial abutment and the reaction sleeve has a second end used as an axial abutment and is supported by this second end, with the interposition of the return spring, against the axial abutment of the pin-shaped stop part. The pin-shaped stop part has a narrow pin section and a wide pin section, with a transition therebetween, the transition being an inclined surface against which the reaction balls come to rest when the selector shaft is actuated in the direction of the principal axis into one of three positions each assigned to a particular shift gate of the change-speed gearbox. The reaction balls are supported centripetally against the wide pin section after being displaced radially along the inclined surface on the pin-shaped stop part when the selector shaft is actuated into a second position lying adjacent to the first position in the direction of the principal axis, and the reaction sleeve is displaced in the direction of the abutment of the return spring by the reaction balls cooperating with the inclined surface of the reaction sleeve, the abutment of the return spring being fixed in terms of motion relative to the pin-shaped stop part. A third position of the selector shaft lies adjacent to a first position in the direction of the principal axis opposite to the second position. The reaction sleeve has an axial stop for contact with the radial guide and the radial guide has a corresponding stop, and the two stops rest against one another when the selector shaft is in that region of the principal axis which is defined by the first position and the third position.
In the gear-shift device according to the invention, the spring force of the return spring is introduced into the sleeve-shaped stop part via the stops of the reaction sleeve and the radial guide when the selector shaft is actuated in the region of the principal axis defined by the second and third position, the reaction balls being bypassed.
This advantageous effect of the stops of the reaction sleeve and the radial guide as regards the freedom from forces of the reaction balls is also maintained in the further development of the gear-shift device according to the present invention in accordance with certain embodiments in which the return spring is used as a centering spring for an unactuated rest position of the selector shaft, for which a third position assigned to a particular shift gate and adjacent to the first position can be provided.
While it does lie within the scope of the invention for the reaction sleeve to have a stop surface for its contact with the radial guide in addition to its inclined surface, the inclined surface in accordance with the embodiment of the gear-shift device according to the invention in accordance with certain embodiment is additionally used as the stop surface.
If, in the gear-shift device according to the invention, the axial stop of the narrow pin section is, according to certain embodiments, designed as an inclined surface to define the third position of the selector shaft, and consequently the line of action of force in the supporting of the spring force is not parallel to the principal axis, it is possible to keep the differences in the diameters of the sleeve-shaped and the pin-shaped stop part small. In the gear-shift device according to the invention, a particularly advantageous path of force from the inclined surface on the reaction sleeve to the inclined surface of the narrow pin section via the reaction balls is achieved in accordance with certain embodiments of the invention.
In an embodiment of the gear-shift device according to the invention which is advantageous as regards the production of the radial guide with the associated inclined stop surface for the reaction sleeve, a guide ring is provided.
In the gear-shift device according to the invention, coordination to achieve freedom of movement for the reaction balls is made possible in accordance with certain embodiments of the present invention.
In the gear-shift device according to the invention, a configuration which is advantageous particularly as regards the adjustability of the stops or abutments on the housing is achieved by certain embodiments of the invention.